Effects of root morphology and physiology on the formation and regulation of large panicles in rice

At present, indica/japonica hybrid rice varieties of the Yongyou series generally show high yield and large panicles, but the physiological mechanism on the formation of large panicles is not clear. It is of great significance to understand the physiological mechanism and regulation of the formation of large panicles in super high-yield rice varieties. In this study, five groups of different rice varieties with significant differences in yield levels were selected as materials to study the contribution of large panicles to rice yield, the physiological changes in roots and canopy during the panicle differentiation stage and the regulation of large panicles by panicle nitrogen fertilizer under field and pot cultivation conditions. The results showed that 1. high-yield indica/japonica hybrid rice varieties were characterized by high spikelet number per panicle and high total number of spikelets. 2. The zeatin (Z) and zeatin riboside (ZR) contents in roots and panicles from spikelet primordium differentiation (SPD) to pistil and stamen formation (PSF), root activity (root dry weight, root oxidation activity, root bleeding rate, root total absorbing surface area and root active absorbing surface area) and non-structural carbohydrate (NSC) accumulation in stems from pollen mother cell meiosis (PMC) to pollen filling (PF) were very significantly and positively correlated with spikelet number per panicle. 3. Compared with 0 N (no panicle nitrogen fertilizer), the number of spikelets per panicle and total spikelets of Yangdao 6 and Yongyou 1540, the Z + ZR contents in panicles and roots during SPD-PSF, and the root activity and NSC accumulation in stems during PMC-PF were significantly improved under LN (panicle nitrogen fertilizer at a rate of 1.2 g pot⁻¹) and MN (panicle nitrogen fertilizer at a rate of 2.4 g pot⁻¹). High Z + ZR contents in young panicles and roots during SPD-PSF and large amounts of root activity (root dry weight, root oxidation activity, root bleeding rate, root total absorbing surface area and root active absorbing surface area) and NSC accumulation in stems during PMC-PF were important physiological factors in the formation of large panicles in super high-yield indica/japonica hybrid rice. Improvements in the above indexes during the panicle differentiation stage are likely contribute to the formation of large panicles and the increase in rice yield.